main(List<String> args) {
  var p = Person('葱葱', 18);
  print(p);
  var p2 = Person2('葱葱2', 18);
  print(p2);
}

// 正常的
class Person {
  String name;
  int age;
  Person(String name, int age) {
    this.name = name;
    this.age = age;
  }
}

// 语法糖
class Person2 {
  String name;
  int age;
  Person2(this.name, this.age);
}
